This invention relates to a yarn winder for uniformly winding yarns all over outer circumferences of core members of balls for golf, baseball and the like without unevenness.
Yarn winders of this kind has been known for example as that disclosed in Japanese Patent Application Laid-open No. 61-211,275 which belongs to the assignee of the present case.
The yarn winder disclosed in the Japanese Patent Application of the prior art comprises as shown in FIGS. 1a-1c a pair of cylindrical rollers 1 extending in a horizontal plane and adapted to be rotated in the same directions and moved in respective axial directions opposite to each other, and a roller 3 in the form of two frustocones connected with their small diameter ends extending in parallel with the cylindrical rollers 1 and being forced with a predetermined force against a spherical body 2 arranged on the cylindrical rollers. With this yarn winder, the cylindrical rollers 1 are rotated in the same directions and moved in opposite axial directions so that the spherical bodies 2 positioned between the cylindrical rollers 1 and the two-frustoconical roller 3 is rotated about an axis in parallel with the cylindrical rollers 1 and two-frustoconical roller 3 in a counterclockwise direction viewed in FIG. 1a and is at the same time rotated about an axis perpendicular to the axes of these rollers 1 and 3 in a counterclockwise direction viewed in FIG. 1b. Such rotation of the spherical body 2 is affected under the action of the two-frustoconical roller 3, while the spherical body 2 is retained in position between these rollers 1 and 2. Therefore, a yarn or rubber yarn 4 fed from a guide groove 3a of the two-frustoconical roller through guide rollers and pulleys with braking means (not shown) is wound substantially uniformly about the overall outer circumference of the spherical body 2.
In such a winder of the prior art, however, as shown in FIG. 1c a radius R.sub.0 of the spherical body 2 is larger than radii R.sub.1 at contacting points 5a between the spherical body 2 and the two-frustoconical roller 3 in the rotation of the spherical body as shown in FIG. 1a. Therefore, a circumferential velocity of the body at the outer end of the radius R.sub.0 is higher than those at the outer ends of the radii R.sub.1. On the other hand, with the integrally formed two-frustoconical roller 3, a circumferential velocity of the guide groove 3a is lower than those at contacting points of the two-frustoconical roller 3 with the spherical body 2. As a result, a pay out velocity of the rubber yarn 4 is considerably lower than the circumferential velocity of the spherical body 2 at the outer end of the radius R.sub.0 so that excessive tensile stresses act on the rubber yarn. Accordingly, there is a tendency of the rubber yarn to be cut due to the excessive tensile stresses with high probability.
In addition, when the spherical body 2 is simultaneously forced to rotate in the two directions shown in FIGS. 1a and 1b, the spherical body is rotated in an upper right hand direction shown by an arrow A in FIG. 1c so that one-half of the two-frustoconical roller 3 on the right side is subjected to a downwardly directing force shown by an arrow B, while a half of the roller 3 on the left side is subjected to an upwardly directing force shown by an arrow C. On the other hand, however, the two halves of the two-frustoconical roller 3 formed in a unitary body could not carry out such a free relative displacement in the external forces acting directions. Accordingly, it is actually impossible to cause the spherical body 2 to rotate in the predetermined manner. It is, therefore, very difficult to wind the rubber yarn 4 uniformly about the entire outer circumference of the spherical body 2.